1. Field of the Invention
This invention relates to a technique for separating and removing fine particles of unburned carbon and other materials present in a desulfurization absorbing fluid after gas-liquid contact in a wet flue gas desulfurizer for removing sulfur oxides from the combustion exhaust gas of a boiler or the like.
2. Description of the Related Art
In a wet flue gas desulfurizer, exhaust gas is cleaned by gas-liquid contact with an absorbing fluid containing lime or the like, so that sulfur oxides (SO.sub.x) and fine particles of unburned carbon and other materials are removed therefrom. The fine particles of unburned carbon and other materials which have passed from the exhaust gas to the absorbing fluid remain in the by-product (e.g., gypsum) separated and recovered from the absorbing fluid and cause a reduction in purity and a reduction in quality due to discoloration.
Conventionally, in order to reduce the content of impurities (i.e., fine particles of unburned carbon and other materials) in gypsum obtained as a by-product to less than a specified level, it has been common practice to concentrate the gypsum present in the absorbing fluid having sulfur oxides (SO.sub.x) absorbed therein by means of a liquid cyclone and thereby reduce the content of unburned carbon on a relative basis. However, since unburned carbon behaves in substantially the same manner as the absorbing fluid, there is a limit in reducing the content of unburned carbon by concentrating the gypsum by means of a liquid cyclone. For example, even if the requirements for the purity of gypsum are met, a reduction in quality due to a deterioration of appearance by discoloration may be unavoidable.
Thus, gypsum obtained as a by-product in wet flue gas desulfurization involves problems such as reduced prices and limited uses due to discoloration caused by impurities comprising fine particles of unburned carbon and other materials.
An object of the present invention is to provide a method and apparatus for the treatment of a desulfurization absorbing fluid which enables fine particles of unburned carbon and other materials to be efficiently removed from the desulfurization absorbing fluid prior to the separation of a by-product so that a by-product (e.g., gypsum) having a low impurity content and showing little discoloration may be separated and recovered from the desulfurization absorbing fluid.